No problem for all the questions, I have been working in solitude on this project with a lot of unknowns, so a lot of trial and error (previously have only used max/msp in laptop sound installations and performance scenarios).
Actually, no back up cards, but I did use the one that I hadn't completely set up yet, so getting it back to where it was isn't that hard. And to be honest i"m used to re-setting these things, its been quite a steep learning curve with lots not working.
The manual I found for puredata (http://en.flossmanuals.net/pure-data/network-data/send-and-receive/) was suggesting the netsend / netreceive objects, so I just took that for granted. At the moment, in its simplest form I would just like the same bang to be sent to all rpi's simultaneously, to that playback start could be synchronised. I assume for this to happen they could all just listen on the same port, and receive the same bang?
I was planning on one of the four rpi as being the router as well as an interface. Is this a bad idea? To be honest getting one to be a router was a huge battle, so if i could just use a router that would be easier. Conveniently those router's you suggested run off 12v, and my system runs of that, so it would be easy to put in the mix. Would the signal be stronger/reach further using a router as opposed to an rpi?
No, not planning on streaming audio. My thought process was that this might be a headache, and take up a bit of CPU. But in all honest its not needed for the project. The main forms of playback would literally be a mono file loaded into a PD patch with synchronised playback, or a PD patch as instrument (ie, sampler/synth type of interface) loaded onto each pi. In either case, they would be controlled via OSC. The instrument version might have been controlled by different ipads/OSC devices.
Too late, have already bought the screens. Part of this decision process was that there is so much that could go wrong in this scenario, that with a touch screen added I could easily trouble shoot in the field. Also, for the instrument patch, the instrument could just be on the screen which would be great.
The original touchscreens, small 2" ish ones, wouldn't work with Jessie, that's the short answer. However, what I wanted to do was to be able to access the HDMI out in order to mirror the screen, so that I could actually see what I was programming. I didn't know when purchasing them that the HDMI out is disabled once they are installed, and its a headache to get them output both to screen and HDMI out. So the 7" screens I figured would easily allow me to program the device in my studio without the need for extra monitors, and could easily be used in the field.
So, I'm pretty sure i can now change to Jessie, as the 7" screens seem easier to work with. The only thing that wouldn't work is the tutorial I have for turning a RPI into a router. But, if that will make things complicated (which if I'm reading between the lines, it might?), then I think powering an external router might be an easier option.
I think Armel in the long run will cause headaches, it does make sense to stay with the newer version, and I think switching to Jessie at this point in time would make sense.
Epic reply. Thoughts welcome!!